Embodiments relate to electric and/or electronic devices, and methods thereof. Some embodiments relate to digital synthesis, for example microwave generation and methods thereof.
Adding a positive square pulse, for example half a nanosecond long, to a substantially similar negative pulse that immediately follows it may refer to a cycle of microwaves including a GHz fundamental frequency. Pulse length may range, for example, between approximately 10 ns and ps's. The process may be repeated to produce more cycles and/or longer pulses. The approach may be desirable for generating high power microwaves (HPM) since the power available may exceed resonant based generation such as magnetron and klystrons.
Transmission lines (TL's) utilizing a relatively thin dielectric film may include relatively smaller impedance and/or include relatively larger breakdown electric fields. Since the pointing vector, which may reference the measure power flow in a TL, is proportional to the electric filed squared, such circuits may correspond to a relatively higher power per unit volume of source. However, using relatively thin dielectric films may increase dissipation in the TL conductors due to the skin depth effect. Such dissipation limits the efficiency and reduces the number of sections that can be added which limits the number of cycles an total pulse length and thus pulse energy.
Photoconductive switches may be used to accommodate a relatively higher switching power. Si back biased junctions, which may be activated with 1.06 micron laser pulses (pulsed YAG laser), may have the current, switching power and speed required to switch relatively thin film TL's. However, using such switches does not minimize dissipation in the TL conductors, for example resulting from relatively thin films.
A charged TL may be discharged with a switch into a matched load impedance in double TL duration to generate the fastest possible discharge and thus pulses with the highest possible power. There have been attempts to produce relatively more cycles by adding TL sections interconnected with switches. Two related circuits may include a frozen wave circuit (Proud et al., “High Frequency Waveform Generation Using Optoelectronic Switching in Silicon”, IEEE Trans on Microwave Theory and Techniques, Vol. MTT-26, No. 3 (1978)), where switches may be all closed at once, and a sequential switch circuit (U.S. Pat. Nos. 5,109,203 and 5,185,586 to Zucker et al.), where the first switch closed is nearest the load with the next switch in line closed at least two transit time later (2τ). Since the energy from the back of the system flows through the closed switches ahead, there exist a cumulative loss in the switches which may reduce the number of sections that may be connected.
A Switch Bypass Source (SBS) circuit (U.S. Pat. Nos. 7,268,641 and 7,365,615 to Zucker et al.) may allow pulses to bypass still-open switches. The first switch closed is the one farthest from the load, and the generated pulse travels in the two outer conductors bypassing the not yet closed switches ahead of it. Cumulative switch loss is thus minimized, more switches may be used to produce relatively more cycles with its attendant larger energy. While SBS increases the number of cycles that can be produced, a second dissipation effect due to skin depth losses becomes important, which results in a new limit on the total number of switches/sections, and thus cycles that can be produced.
An SBS circuit may partially addresses skin depth dissipation in the TL's, which is proportional to the penetration depth and inversely proportional to the TL's separation, for example the thickness of a relatively thin film. Skin depth dissipation in TL's may be partially addressed in U.S. Pat. Nos. 7,268,641 and 7,365,615 to Zucker et al. in either of two ways. In the first, the dielectric spacing of the unswitched lines is increased uniformly in all section to a value twice the dielectric spacing of the switched lines. In the second, the overall spacings taper downward in the direction of the load. These two approaches and variations thereof only marginally improve on the basic circuits in the resulting number of pulses that can be practically produced in reasonable volumes and/or efficiency.
Therefore, in order to be able to use more sections which are needed to produce more cycles and thus longer microwave pulses without prohibitive losses, reduced power, and/or increased apparatus volume, there is a need for electronic and/or electrical devices, and methods thereof.